1. Field of the Invention
The present invention relates to radio telecommunications systems, and more particularly, to radio local loop systems.
2. Brief Description of the Related Art
A radio local loop (RLL) system is a wireless telecommunications system, wherein fixed subscriber units or terminals communicate with the system over an air interface. Such radio systems are connected to private or public switched telephone networks and include a number of radio domains, each radio domain containing one or more radio stations (RS), or base stations. Each radio station controls the wireless communication links with any number of fixed subscriber units located in a corresponding geographical coverage area. A control unit for each radio domain stores and maintains a subscriber list containing the identification codes for each fixed subscriber unit assigned to that radio domain.
A fixed subscriber unit is typically either immobile or limited in its ability to be moved during operation (e.g., as is the case with a cordless telephone). All communication with the fixed subscriber unit is handled through the radio station servicing the corresponding coverage area in which the fixed subscriber unit is located. The fixed subscriber unit has a transceiver and an antenna for transmitting and receiving telecommunications data to and from the radio station via the air interface, over at least one pre-assigned radio channel, wherein a radio channel is defined by any number of different channel access schemes.
One such channel access scheme is known in the art as time division multiple access (TDMA). In a TDMA based system, such as a TDMA based RLL system, each of a number of frequency carriers is subdivided into a number of time slots. By subdividing each frequency carrier into multiple time slots, the traffic capacity of the system is substantially increased, as each of a number of fixed subscriber units are able to communicate over a single frequency carrier by limiting the time during which each transmits or receives data and control information to one or more assigned time slots.
A TDMA based system may further be characterized as either a time division duplex (TDD) system or a frequency division duplex (FDD) system. In a TDMA/FDD system, each frequency carrier is subdivided into time slots as described above. However, certain frequency carriers are dedicated to carrying downlink traffic (i.e., data and/or control information being transmitted from a radio station to a fixed subscriber unit), while other frequency carriers are dedicated to carrying uplink traffic (i.e,. data and/or control information being transmitted from a fixed subscriber unit to a corresponding radio station). In contrast, each frequency carrier in a TDMA/TDD based system handles both uplink and downlink traffic, such that approximately half of the time slots associated with a given frequency carrier are predesignated for carrying downlink traffic, while the remaining time slots associated with that frequency carrier are predesignated for carrying uplink traffic. A RLL system that employs the well-known Digital Enhanced Cordless Telecommunications (DECT) standard is an example of a TDMA/TDD based system.
In recent years, the demand for wireless radio communication services, and in particular, fixed radio communications services, has increased at an extraordinary rate. This is problematic because radio network resources are generally limited, thereby limiting both the geographic area that a system is capable of covering and limiting the amount of traffic (i.e., the traffic load) that a system is capable of handling. One way to address this problem is to construct new networks and/or to expand existing networks.
When the topology of a radio system is changed, such as adding new radio stations or radio domains to support increased traffic demand, the antennas at a number of fixed subscriber units must be adjusted or redirected towards the new radio station. In addition, the affected subscriber units must be reassigned to the new radio domain corresponding to the new radio station. This involves reallocating or re-registering each of the affected fixed subscriber units to the subscriber list maintained for the new radio domain, and removing each of these fixed subscriber units from the subscriber list associated with the radio domain in which they are currently allocated.
Presently, the addition of a new radio station or radio domain requires much effort, including the manual adjustment and reallocation of the affected subscriber units. And, as one skilled in the art will readily appreciate, this is extremely expensive, particularly if the RLL system is constantly undergoing network reconfiguration and/or network expansion to include the addition of new radio domains. Accordingly, in a fixed RLL system, it would be desirable to have a method and communication system that can automatically reallocate a subscriber unit to a different radio domain but without the need to perform complex reallocation and/or readjustment procedures, or the expense associated therewith.
The present invention generally relates to a method and communications system that automatically reallocates subscriber units in a RLL system when the radio system topology is changed, without expending the costly and time consuming efforts needed to manually readjust antennas.
In accordance with one aspect of the present invention, the RLL system can automatically redirect a fixed subscriber unit, particularly the antenna associated with the fixed subscriber unit, so that it transmits and receives through a traffic channel associated with a different radio domain. In a preferred embodiment, the fixed subscriber unit maintains a traffic channel register that identifies the time slot, frequency, radio station number, scan angle, and radio domain through which the fixed subscriber unit is to communicate. By transmitting an identification code of a second radio domain, thereby changing the radio domain value, an operator can directly or remotely reassign the fixed subscriber unit to the second radio domain. A control unit associated with the second radio domain will store information in its subscriber list concerning the reassigned fixed subscriber unit while the control unit of the first domain removes such information.
In accordance with another aspect of the present invention, the RLL system can begin reallocating a fixed subscriber unit from a first radio domain to a second radio domain by sending a code identifying the second radio domain to the fixed subscriber unit. In response to receiving the code, an antenna associated with the fixed subscriber unit is directed towards the second radio domain. While varying the antenna scan angle, the fixed subscriber unit determines a signal quality value for each communication channel, wherein the channel is defined by a frequency, a time slot, a radio station, a radio domain, and an antenna scan angle. If at least one communication channel in the second radio domain exhibits superior signal quality values than communication channels in the first radio domain, then the fixed subscriber unit is reallocated to the second radio domain.
The present invention provides advantages over the prior art. First, when the radio system topology is changed, a fixed subscriber unit can be easily adjusted or redirected by transmitting a different radio domain value. Second, using an improved method for dynamic channel selection, the fixed subscriber unit will automatically adjust itself to a radio channel based on the registered signal quality factor. Thus, fixed subscriber units can be automatically reallocated to different radio domains without expending the costly and time consuming efforts needed to manually readjust each antenna.